1. Field of the Invention
The present invention relates to, for example, a transistor, a semiconductor device, and manufacturing methods thereof. The present invention relates to, for example, a display device, a light-emitting device, a lighting device, a power storage device, a memory device, a processor, an imaging device, and an electronic device. The present invention relates to methods for manufacturing an oxide, a display device, a liquid crystal display device, a light-emitting device, a memory device, a processor, an imaging device, and an electronic device. The present invention relates to methods for driving a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a memory device, a processor, an imaging device, and an electronic device.
Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. One embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter.
In this specification and the like, a semiconductor device refers to any device that can function by utilizing semiconductor characteristics. A display device, a light-emitting device, a lighting device, an electro-optical device, a semiconductor circuit, and an electronic device include a semiconductor device in some cases.
2. Description of the Related Art
A technique for forming a transistor by using a semiconductor over a substrate having an insulating surface has attracted attention. The transistor is applied to a wide range of semiconductor devices such as an integrated circuit and a display device. Silicon is known as a semiconductor applicable to a transistor.
As silicon which is used as a semiconductor of a transistor, either amorphous silicon or polycrystalline silicon is used depending on the purpose. For example, in the case of a transistor included in a large display device, it is preferable to use amorphous silicon, which can be used to form a film on a large substrate with the established technique. In the case of a transistor included in a high-performance display device where driver circuits are formed over the same substrate, it is preferable to use polycrystalline silicon, which can be used to form a transistor having high field-effect mobility. As a method for forming polycrystalline silicon, high-temperature heat treatment or laser light treatment which is performed on amorphous silicon has been known.
In recent years, transistors including oxide semiconductors (typically, In—Ga—Zn oxide) have been actively developed.
Oxide semiconductors have been researched since early times. In 1988, there was a disclosure of a crystal In—Ga—Zn oxide that can be used for a semiconductor element (see Patent Document 1). In 1995, a transistor including an oxide semiconductor was invented, and its electrical characteristics were disclosed (see Patent Document 2).
In addition, a transistor including an amorphous oxide semiconductor is disclosed (see Patent Document 3). An oxide semiconductor can be formed by a sputtering method or the like, and thus can be used for a semiconductor of a transistor in a large display device. A transistor including an oxide semiconductor has high field-effect mobility; therefore, a high-performance display device where driver circuits are formed over the same substrate can be obtained. Moreover, there is an advantage that capital investment can be reduced because part of production equipment for a transistor including amorphous silicon can be retrofitted and utilized.
Recent research and development results show that using a crystalline oxide semiconductor increases the reliability of a transistor as compared to the case of using an amorphous oxide semiconductor (Non-Patent Document 1).
It is also disclosed that a transistor having a high field-effect mobility can be obtained by a well potential formed using an active layer including an oxide semiconductor (see Patent Document 4). It is known that a transistor including an oxide semiconductor has an extremely low leakage current in an off state. For example, a low power consumption CPU and the like utilizing a characteristic of a low leakage current of the transistor including an oxide semiconductor are disclosed (see Patent Document 5).